1. Field of the Invention
This invention relates to a heat treatment apparatus for metals or metal articles, and more particularly to a heat treatment apparatus comprising a fluidized-bed furnace, and a gas cooling chamber disposed above the fluidized-bed furnace, and a circuit arrangement for circulating together or separately the heated furnace gas in the fluidized-bed furnace and the cooling fluid in the gas cooling chamber, and wherein heating and cooling are effected continuously.
2. Description of the Prior Art
A conventional heat treatment apparatus using a fluidized-bed furnace as a heating furnace is disclosed in, for example, Japanese Laid-Open-To-Public Specification No. 57-152417. According to this specification, there is disclosed a heat treatment furnace having a pair of independent heat treatment furnaces for high and low temperature uses installed in juxtaposition, and arranged such that the furnace gas discharged from the high temperature furnace is allowed to pass through heat exchange pipes mounted in the low temperature furnace so as to conduct heat exchange with the fluidized-bed inside the low temperature furnace, and is then pressurized by means of a fan to allow it to circulate again into the high temperature furnace. This conventional type heat treatment apparatus is intended to achieve the reuse of waste heat and exhaust gases, and also aims at stabilization of the furnace gas in the heat treatment apparatus for high temperature use; that is, the volume and composition of gases in the furnace. This conventional heat treatment apparatus, however, needs to operate always both the high and low temperature furnaces at the same time, since if only the high temperature furnace is operated the furnace gas kept at a high temperature is drawn into the furnace gas circulating fan without conducting heat exchange thus causing a damage of the fan by the high temperature furnace gas. Therefore, it is uneconomical not to use both the high and low temperature furnaces at the same time.
Moreover, a further conventional heat treatment furnace is well-known, which uses a vacuum furnace as a heat treatment furnace utilized for bright hardening or bright quenching, bright annealing and bright tempering of steels, and for sintering of metals. In this heat treatment apparatus, however, since heat treatment is conducted under a vacuum condition, a special discharge device and a vacuum container etc. are required, and so the apparatus per se becomes necessarily large in size and expensive in cost. Further, this type of heat treatment apparatus is also disadvantageous in that when cooling the heat-treated articles, thermally insulated walls and door of the furnace need to be cooled at the same time which results in deteriorated heat efficiency at the time of reheating. The heat treatment apparatus using a vacuum furnace is still further disadvantageous in that, in the respect of heat treatment performance aspect, articles are subjected to non-uniform heat treatment, and it takes sometimes a long time to conduct heat treatment.